Merge pull request #1405 from Friendseeker/remove-xor-hash-1

[1.x] Use `hashCode` instead of XOR hash in `extraHash` computation

internal/zinc-core/src/main/scala/sbt/internal/inc/Incremental.scala

@@ -886,7 +886,7 @@ private final class AnalysisCallback(
                 val externalParentsAPI = externalParents.map(analysis.apis.externalAPI)
                 val internalParentsAPI = internalParents.map(analysis.apis.internalAPI)
                 val parentsHashes = (externalParentsAPI ++ internalParentsAPI).map(_.extraHash())
-                parentsHashes.fold(currentExtraHash)(_ ^ _)
+                (parentsHashes + currentExtraHash).hashCode()
               case None => currentExtraHash
             }
           }